1. Field of the Invention
The present invention generally relates to vibration induced atomizers and, in particular, to vibration induced droplet and vapor atomizers that may be utilized in heat transfer applications, among others.
2. Description of the Related Art
Atomizers are commonly used in a variety of processes and devices. Atomizers, basically, are concerned with breaking up materials, typically liquids, into very small droplets, or particles. Designers of these devices have created a wide range of atomizing apparatuses and methods. For example, some atomizers collide a gaseous stream into a liquid stream to break the liquid stream into "atomized" droplets. Ultrasonic atomizers are also common. Ultrasonic atomizers utilize ultrasonic waves, typically in the megahertz frequency range, to atomize a liquid by focusing the ultrasonic waves on the free-surface of the liquid. In other applications, the ultrasonic vibrations are used to force liquid through an array of holes, each of the holes being on the order of tens of microns in size, to create a spray of atomized droplets. Additionally, other types of atomizers are well known in the art and used in a variety of applications.
Prior art atomizers, however, typically require some type of fluid piping and fluid supply to operate or use bulky ultrasonic transducers. Indeed, most atomizers are designed to constantly inject an atomized liquid into a system. An atomizer that does not require such fluid input to the system, but that is self-contained, may be very useful in many applications, such as in heat transfer devices. Additionally, an atomizer that combines rapid (even near instantaneous) atomization of a discrete fluid droplet will be advantageous in a wide variety of applications. Heat transfer is one potential application for such a new atomizer.
Thermal management is a critical technology for many of today's high performance devices. Particularly, thermal management is critical to high performance vehicles and engines as well as vehicles used in a microgravity environment, such space vehicles, satellites, and the like. In hypersonic flight, for example, the leading edge of an airfoil is subjected to intense frictional heating that can raise the temperature of the airfoil's skin to over the melting point. In advanced turbine engines, blade and vane cooling is critical to prevent melting, erosion, and/or structural failure of turbine blades and vanes. In a microgravity environment, spacecraft power plants are cooled properly for efficient operation. Similarly, the living environment of a spacecraft must be maintained within the proper temperature range. Sensitive scientific instruments used in space, such as low temperature charge coupled diode (CCD) imagers, are maintained at a constant uniform temperature in order to work effectively.
In addition, there is an ever-increasing demand for power in space missions, such as the Space Lab project. Increasing the size of power plants aboard such spacecraft brings with it an even larger thermal management problem associated with the waste heat generated by the system. Thus, effective cooling techniques are necessary in all of these applications.
One popular technique for thermal control in aerodynamic applications is film cooling. In this technique, air is injected from small holes in the surface of the object to be cooled to form a thin film of air flowing on the surface. The air film cools the surface and effectively insulates it from the high-temperature gas flowing past it.
Another popular technique for thermal management in these various applications is the use of a "heat pipe." These devices are often used in microgravity and aerodynamic applications because they can accommodate a wide range of operating temperatures, can transport large amounts of heat, and can operate independently of gravity. In addition, relatively high heat transfer rates can be achieved by heat pipes, which is typical of a phase-change heat transfer device.
Heat pipes are relatively simple devices. Conceptually, heat pipes passively transfer heat from a heat source to a heat sink, where the heat is dissipated. The heat pipe itself is a vacuum-tight vessel, typically cylindrical in shape, that houses a working fluid. The working fluid typically comprises methanol, ethanol, water, or another similar fluid. The vessel also houses a wick element spanning the length of the vessel. As heat is directed into one end of the heat pipe, the working fluid vaporizes, creating a pressure gradient along the length of the pipe. This pressure gradient forces the vapor to flow along the pipe to the cooler end, where the vapor condenses, giving up its latent heat of vaporization. The working fluid is then absorbed by the wick element and moved by capillary forces back to the heated end of the heat pipe.
While heat pipes have many advantages, heat pipes also have critical limitations. In aerodynamic applications, for example, the heat pipes must be capable of operating in the high g-loads typical of a maneuvering fighter aircraft. Regardless of the application, however, a major limitation of heat pipes is that the amount of heat transfer performed by these devices is strictly governed by the liquid flow rate produced by the capillary pumping in the wicking material of the heat pipe. Thus, there exists a need for improved apparatuses and methods which address these and other shortcomings of the prior art.